1. Field of the Invention
The present invention relates to apparatuses capable of performing frequency adjustment by etching elements formed on a wafer, or relates to apparatuses capable of performing frequency adjustment by applying a frequency adjusting material to elements formed on a wafer.
2. Description of the Related Art
In a conventional frequency adjusting method, the frequency of a piezoelectric element is adjusted by etching the piezoelectric element with an ion beam. To achieve higher productivity in using this method, a plurality of elements are formed or arranged on a wafer so that the frequencies of the plurality of elements can be adjusted at the same time. In this frequency adjusting method, to prevent the wafer other than areas of desired elements from being irradiated with the ion beam, it is necessary that the wafer be masked with a pattern mask. However, when each element is small in size, it is difficult to selectively apply the ion beam only to a desired element. Therefore, a plurality of elements may be grouped together as a single irradiation area to be irradiated.
When such small elements are closely arranged on the wafer, it is necessary to apply the ion beam uniformly to the entire surface of the wafer. However, depending on the size or shape of a hole in the pattern mask, areas adjacent to an irradiation target area may be irradiated with the ion beam, or the edge of the irradiation target area may not be sufficiently irradiated with the ion beam.
Japanese Unexamined Patent Application Publication No. 2002-26673 discloses a frequency adjusting method in which the frequency of each piezoelectric element is adjusted by applying an ion beam to a plurality of electrodes formed on a surface of a piezoelectric substrate, and thereby etching the electrodes. This method involves determining a correlation between an ion-beam irradiation time and the amount of frequency change, measuring the frequency of each element on the piezoelectric substrate, determining the amount of frequency adjustment for each element on the basis of a difference between the measured frequency and a target value, determining the ion-beam irradiation time for each element on the basis of the determined amount of frequency adjustment by using the correlation, and applying an ion beam to each element during the determined irradiation time.
Japanese Unexamined Patent Application Publication No. 2004-56455 discloses a frequency adjusting apparatus capable of adjusting the frequencies of piezoelectric elements by performing ion beam etching in a vacuum chamber. The frequency adjusting apparatus includes a piezoelectric substrate having a plurality of electrodes formed on its surface; a base plate having an opening for selectively allowing the plurality of electrodes on the piezoelectric substrate to be exposed; an ion source configured to apply an ion beam simultaneously to the plurality of electrodes exposed from the opening in the base plate; a protective plate configured to protect, from being etched, a region around the opening in the base plate to which the ion beam is applied; shutter mechanisms provided as many as the number of the electrodes exposed from the opening in the base plate, and capable of being independently driven; and a masking plate for blocking the ion beam leaking through gaps between the shutter mechanisms.
Additionally, as illustrated in FIG. 8, FIG. 9A, and FIG. 9B, there is a conventional frequency adjusting apparatus capable of simultaneously adjusting the frequencies of a plurality of elements arranged perpendicularly to a wafer conveying direction. In this apparatus, a wafer 50, on which a plurality of elements 51 are arranged in a matrix, is conveyed by a conveying unit (not shown) in a wafer conveying direction indicated by an arrow, as shown in FIG. 8. The wafer 50 passes under a pattern mask 52 having a mask hole 53. The mask hole 53 is a slit-like (i.e., elongated) hole allowing a column of elements arranged perpendicularly to the conveying direction of the wafer 50 to be exposed. A plurality of shutters 54 (e.g., six shutters 54 in FIG. 8) are arranged on the pattern mask 52. Each of the shutters 54 is independently actuated with respect to the mask hole 53 in the wafer conveying direction. By selectively covering the slit-like mask hole 53 with the plurality of shutters 54, an irradiation time during which each of the elements 51 is irradiated with an ion beam can be adjusted.
In the case of Japanese Unexamined Patent Application Publication No. 2002-26673, a pattern mask having mask holes corresponding to the respective positions of the electrodes is disposed on the piezoelectric substrate. These mask holes are spaced apart from each other, and the ion beam cannot be applied to regions where there are no mask holes. Therefore, this pattern mask is not suitable for use in irradiating small elements closely arranged on the piezoelectric substrate. Additionally, since a rotatable disk-shaped shutter having a double-layered structure is used, it takes time to change the shutter position. Moreover, since the shutter may pass through an opening during rotation, the accuracy of frequency adjustment may be degraded.
In the case of the frequency adjusting apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-56455, the ion beam is blocked by the masking plate disposed directly above a wafer. However, the shape of holes in this masking plate is not suitable for processing small elements arranged closely on the wafer, as in the case of Japanese Unexamined Patent Application Publication No. 2002-26673 described above.
In the case of the apparatus illustrated in FIG. 8, the shutters 54 for covering the slit-like mask hole 53 may be arranged side by side with gaps between adjacent ones, as shown in FIG. 9A, or stacked in a vertical direction, as shown in FIG. 9B. In the case of FIG. 9A, the ion beam enters through the gaps between adjacent shutters 54. This may cause adjustment errors when the elements 51 are closely arranged on the wafer 50. In the case of FIG. 9B, since a masking shape is determined not only by the pattern mask 52 but also by the adjacent shutters 54, a masking position (i.e., distance from the wafer 50) is not constant. Since the ion beam tends to spread out, a change in masking position may cause a change in the amount of spreading of the ion beam. As a result, the amount of etching in adjacent areas or the amount of etching at the edge of a target area may be reduced.